Switching voltage stabilizer. Encyclopedia of radio electronics and electrical engineering
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Due to their high efficiency, switching voltage stabilizers have recently become more widespread, although they are usually more complicated than traditional ones and contain a larger number of elements. However, if you do not impose excessive requirements on the stability and ripple of the output voltage, then their circuit can be greatly simplified. So, for example, a stabilizer with an output voltage lower than the input voltage can be assembled on only three transistors (see figure), two of which (VT1, VT2) form a key regulatory element, and the third (VT3) is an error signal amplifier.
The device operates in self-oscillating mode. The positive feedback voltage from the collector of the transistor VT2 (it is composite) through the capacitor C2 enters the base circuit of the transistor VT1. Transistor VT2 periodically opens up to saturation with current flowing through resistor R2. Since the base current transfer coefficient of this transistor is very large, it saturates at a relatively small base current. This allows you to choose the resistance of the resistor R2 rather large and, therefore, increase the transfer coefficient of the regulating element. The voltage between the collector and emitter of a saturated transistor VT1 is less than the opening voltage of the transistor VT2 (in a composite transistor, as you know, two p-n junctions are connected in series between the base and emitter codes), therefore, when the transistor VT1 is open. VT2 is securely closed.
The element of comparison and the amplifier of the error signal is a cascade on the transistor VT3. Its emitter is connected to a reference voltage source - a zener diode VD2. and the base - to the output voltage divider R5-R7.
In switching stabilizers, the control element operates in the key mode, therefore, the output voltage is regulated by changing the duty cycle of the key. In the device under consideration, transistor VT2 controls the opening and closing of the transistor VT3 according to the signal of the transistor VT1. At the moments when the transistor VT2 is open, in the inductor L1, due to the flow of load current, electromagnetic energy is stored. After closing the transistor, the stored energy through the diode VD1 is given to the load. The output voltage ripple of the stabilizer is smoothed out by the L1C4 filter.
Despite its simplicity, the stabilizer has a fairly high efficiency. Thus, at an input voltage of 24 V, an output voltage of 15 V, and a load current of 1 A, the measured efficiency was 84%.
The inductor 1.1 is wound on a K26X16X12 ring made of ferrite with a magnetic permeability of 100 wire with a diameter of 0.63 mm and contains 100 turns. The inductance of the inductor at a bias current of 1A is about 1 mH. The characteristics of the stabilizer are largely determined by the parameters of the VT2 transistor and the VDI diode. speed of which should be as high as possible.
Note. In the stabilizer, you can use domestic transistors KT825G (VT2), KT313B, KT3107B (VT1), KT315B, KT3102V (VT3), a KD213 diode (VD1) and a KS168A (VD2) zener diode.
Literature
- Radio 5, 1985, p.64
- Jednoduchy impulsni stabilizator naptti.- Sdelovaci technika, 1984, N8, str. 283.
Publication: N. Bolshakov, rf.atnn.ru
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